Electrical machine with double-sided lamination stack

ABSTRACT

The machine includes a rotor with an inner rotor core and an outer rotor core and a double-sided stator with an inner stator side and an outer stator side. The double-sided stator is concentrically disposed between the inner rotor core and the outer rotor core of the wind turbine generator. The double-sided stator is configured to enable at least a portion of magnetic flux to be shared between the inner stator side and the outer stator side. Examples of particularly useful embodiments for the machine include wind turbine generators and ship propulsion motors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application includes subject matter that is related to U.S. patentapplication Ser. No. (Applicant's Docket No. 148901-1), entitled“ELECTRICAL MACHINE WITH DOUBLE-SIDED STATOR”, filed concurrentlyherewith, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to wind turbine generators andship propulsion motors.

Wind is usually considered to be a form of solar energy caused by unevenheating of the atmosphere by the sun, irregularities of the earth'ssurface, and rotation of the earth. Wind flow patterns are modified bythe earth's terrain, bodies of water, and vegetation. The terms windenergy or wind power, describe the process by which the wind is used togenerate mechanical power or electricity.

Typically, wind turbines are used to convert the kinetic energy in thewind into mechanical power. This mechanical power may be used forspecific tasks (such as grinding grain or pumping water) or a generatormay convert this mechanical power into electricity. A wind turbineusually includes an aerodynamic mechanism for converting the movement ofair into a mechanical motion, which is then converted with a generatorinto electrical power. Power output from the generator is proportionalto the cube of the wind speed. As wind speed doubles, the capacity ofwind generators increases almost eightfold.

The majority of commercially available wind turbines utilize geareddrive trains to connect the turbine blades to the wind generators. Thewind turns the turbine blades, which spin a shaft, which feeds into agear-box and then connects to a wind generator and makes electricity.The geared drive aims to increase the velocity of the mechanical motion.The drawback of a geared drive is that it reduces the reliability of thewind turbine and increases the noise and cost of the wind turbine.

A few wind turbines utilizing direct-drive generators are alsocommercially available. The large diameters of the direct drivegenerators present formidable transportation and assembly challenges,both at the factories and at the wind turbine installation sites. As thewind turbine industry matures and technology improves, larger powerratings will be required to continue the downward push in the cost ofenergy. Standard power ratings for land-based turbines are expected tobe 3 MW or greater in the next few years, and the offshore turbines areexpected to be 5 MW or greater.

For the wind turbines to evolve to higher power ratings, conventionalapproaches typically include an increase in the direct-drive generatordiameter or axial (stack) length. Increasing the diameter is preferredfrom a purely generator electromagnetic perspective, but is notattractive from the transportation, frame, and assembly perspectives,especially for land-based turbines. Increasing the axial length of thegenerators, while maintaining the diameter to be less than approximately4 meters, alleviates the land-based transportation issue, but results incomplex and costly frame structures with long axial lengths.

It is therefore desirable to provide cost-effective wind turbines ofincreased power ratings and reduced diameters.

BRIEF DESCRIPTION OF THE INVENTION

Briefly, in accordance with one embodiment of the present technique, awind turbine generator includes a rotor with an inner rotor core and anouter rotor core. The outer rotor core is inverted with respect to theinner rotor core, according to the aspects of present technique. Thewind turbine generator also includes a double-sided stator with an innerstator side and an outer stator side. The double-sided stator isconfigured to enable all or a portion of magnetic flux to be sharedbetween the inner stator side and the outer stator side.

In accordance with another aspect of the present technique, a shippropulsion motor is provided. The motor includes a rotor with an innerrotor core and an outer rotor core, and a double-sided stator with aninner stator side and an outer stator side. The inner stator side andthe outer stator side include a double-sided lamination stack. Thedouble-sided stator is concentrically disposed between the inner rotorcore and the outer rotor core of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a sectional view of a wind turbine including anexemplary direct-drive double-sided permanent magnet (PM) generatoraccording to aspects of the present technique;

FIG. 2 illustrates a sectional view of a direct-drive double-sidedflux-sharing PM generator of FIG. 1;

FIG. 3 illustrates a close up view of the direct-drive PM generator ofFIG. 2 with the air cooling passages;

FIG. 4 illustrates a sectional view of a double-sided stator of the PMgenerator useful for the embodiments of FIGS. 1-3;

FIG. 5 illustrates a close-up view of the double-sided stator of FIG. 4;

FIG. 6 illustrates a cross-sectional view of the double-sided stator andinner and outer rotors;

FIG. 7 illustrates the magnet flux paths in the double-sided stator andinner and outer rotors at one instant of time;

FIG. 8 illustrates an exemplary embodiment with liquid cooling channelsin the arrangement of FIG. 2; and

FIG. 9 illustrates a portion of an exemplary ship propulsion motor witha double-sided lamination stack for the double-sided stator inaccordance with aspects of present technique.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes different embodiments for double-sidedgenerators that are particularly useful for direct-drive wind turbinesand ship propulsion motors. The different direct-drive configurationsfor wind turbines described herein below are based upon a double-sided,radial-flux, synchronous electrical machines. Although permanent magnet(PM) machines are described and shown for the purpose of illustration,other electrical machines such as wound field synchronous machines canalternatively be used. These configurations contribute towards achievingcost-effective wind turbines of increased power ratings (>2.0 MW) andare especially advantageous for land-based applications where theoutside diameter may be constrained by transportation limitations.

Turning now to the figures, FIG. 1 is a diagrammatic representation of asectional view of a wind turbine 10 with an exemplary embodiment of adirect-drive double-sided PM generator 12. The PM generator 12 of thewind turbine 10 includes at least two concentric air gaps (not shown inFIG. 1 and discussed later in reference to FIG. 2), thereby effectivelyconverting the PM generator 12 into two concentric generators. Thus, itwould be appreciated by those skilled in the art that for the same totalenvelope defined by the outside diameter and axial length, the PMgenerator 12 can produce considerably more power output than as asingle-sided generator. In practice, thus a 2 MW single-sided generatormight be replaced by a double-sided generator capable of producing 3-3.6MW for the same total diameter and axial length. Equivalently, a 3 MWsingle-sided PM generator having a diameter of 6 meters might bereplaced with a double-sided generator of the same axial length withonly a 4.3 meter diameter, thereby enabling land-transportation of theentire generator as one unit.

Referring again to FIG. 1, the PM generator 12 is mounted on a nacellemain frame 36 via a main shaft and bearing assembly 56. The nacelle mainframe 36 is further mounted to a tower 38 through a conventional yawbearing and gear drive system (not shown). More detailed features of thePM generator 12 are described herein below with reference to FIG. 2. Arotor blade hub 44 connects the wind turbine rotor blades 42 to the PMgenerator 12. A rotor hub cover 49 contains the wind turbine rotorblades 42 and other turbine rotor components. A nacelle cover 50 is alsoprovided and it typically protects the components inside the nacellefrom the environment.

FIG. 2 illustrates a sectional view of a direct-drive double-sidedflux-sharing PM generator of FIG. 1. The PM generator 12 includes arotor 14 (generator rotor) with an outer rotor core 16 with outerpermanent magnets 18 and an inner rotor core 20 with inner permanentmagnets 22. The outer rotor core 16 is inverted with respect to theinner rotor core 20. The permanent magnet generator 12 also includes adouble-sided stator 24 with an outer stator side 26 with an outer statorwinding (coils) 28 and an inner stator side 30 with inner stator winding(coils) 32. It will be well understood by one skilled in the art thatthe stator 24 is concentrically disposed between the outer rotor core 16and the inner rotor core 20. The outer stator side 26 and the innerstator side 30, thus contribute to the at least two concentric air gaps62, 64 (the inner stator side 30 and the inner rotor core 20 define aninner air gap 64 and the outer stator side 26 and the outer rotor core16 define an outer air gap 62). In a specific embodiment as illustratedin FIG. 2, the outer and inner stator sides 26 and 30 are typicallyconstructed of a single double-sided lamination stack 66 that is boltedaxially by axial bolts 68 to the stationary frame 34. Steel coreplates82 between both sides of the lamination stack 66 and the heads of theaxial bolts 68 provide uniform compression of the stack from the axialbolts 68. The double-sided stator 24 is thus configured to enable atleast a portion (and in some embodiments all) of the magnetic flux to beshared between the inner stator side 26 and the outer stator side 30.

Optional outer rotating seal 84 located between the stationary frame 34and the rotor 14 provides further protection of the components of thedouble-sided stator 24 and rotor 14 from the environment. An optionalinner seal 86 provides sealing between the stator and rotor componentsand the corresponding frame structures 34 and 52. The seals arepreferably of a labyrinth or brush-type seal.

In operation, the power output of the double-sided stator 24 iscontrolled by a power converter unit (not shown) capable of full powerconversion. The stator 24 is connected to a stationary frame 34, whichmay include structural stiffening members or ribs 35. A rotor shaft 46connects to the rotor 14 via a rotating frame 52 at one end and to therotor blade hub flange 54 on the other end, which connects to a turbinerotor blade hub (44 in FIG. 1). The rotating frame 52 may also includestructural stiffening members or ribs 53. The generator rotor shaft 46is mounted on a bearing assembly, consisting of two main bearings, frontmain bearings 58 and rear main bearings 60. Although two main bearingsare illustrated, alternative bearings configurations, including a singlemain bearing, are possible. The bearings are mounted on a stationaryinner shaft 33, that mounts to the nacelle main frame 36 via main frameflange 80. It will be appreciated by those skilled in the art, that themain bearing and shaft diameters may be sized accordingly with the meansfor hub access; e.g., larger-diameter main bearings (about 1.5 meters ormore, for example) would facilitate hub access. The use of lower-costsmall diameter bearings less than or equal to about 1.0 meter, forexample, would likely require hub access through access port(s).

FIG. 3 is a detailed side-sectional view of an air-cooled arrangement inthe double-sided flux sharing PM generator 12 of FIG. 2. As illustrated,a plenum 88 is attached to the stationary frame 34 of the PM generator12. Through the plenum 88 cooling ducts 90 are provided into the statorand rotor. The air passages as described hereinafter describe the flowof air in the cooling duct. The cooling air is passed axially throughthe cooling duct in the double-sided stator. The cooling duct may belocated between at least two adjacent stator coils of a respectivestator slot for passing of the cooling air (as shown by passages 112 and114 in FIG. 6). A cooling air passage 92 depicts the exit of cooling airfrom the stator and rotor into a cooling air passage inlet 94 throughthe rotor frame and a cooling air passage inlet through the stationaryframe 34. Additionally a sealed passage 98 may be provided for passageof cooling air through the rotor frame. An inlet 100 and an exhaust 102are provided for the cooling air in the above arrangement. Note thatalternative air flow paths are possible, including air flow in thereverse direction from illustrated.

FIG. 4 is a sectional view of double-sided stator 24 with outer statorside 26 and the inner stator side 30 disposed about the stationary frame34. FIG. 4 also illustrates the front main bearings 58 and the rear mainbearings 60 and the stationary shaft 33.

FIG. 5 is a close-up view of the double-sided stator of FIG. 4 disposedabout the stationary frame 34 and showing the outer stator windings(coils) 28, inner stator windings (coils) 32, axial bolts 68 and outerstator tooth (teeth) 104. Air cooling passage 90 is also shown whichallows the cooling air to flow into the double-sided stator and rotor

FIG. 6 is a cross-sectional view of the double-sided stator and innerand outer rotors. The illustration shows the outer rotor core 16 withouter permanent magnets 18 and an inner rotor core 20 with innerpermanent magnets 22. The outer and inner stator tooth (teeth) aredenoted generally by reference numerals 104 and 106 respectively and theouter stator winding (coils) 28 and the inner stator winding (coils) 32are retained respectively by the outer stator coil retaining wedge 108and inner stator coil retaining wedge 110. The double-sided stator asdescribed herein above contributes the outer air gap 62 and inner airgap 64. The structural integrity of the stator is achieved throughcompression of the lamination stack 66, via numerous axial bolts 68located in the stator yoke 116. The bolt bodies (shafts) (not shown) andat least one end are insulated from the laminations and frame structuresto avoid induced electrical currents and resulting losses and heating.In one example, at least one bolt per slot is used; e.g., with boltholes 69 as illustrated in FIG. 6. It would be appreciated by thoseskilled in the art that the bolt hole positions may vary. In a specificexample the bolt hole positions may be aligned with stator teeth. Alsoillustrated are cooling air passages as described herein above, thecooling air passage 112 between outer stator windings and the coolingair passage 114 between the inner stator windings.

FIG. 7 illustrates the shared magnet flux paths or flux lines 130 whichflow radially in the double-sided stator and permanent magnets, and flowpredominantly circumferentially in the inner and outer rotor core of thePM generator 12 at any one instant of time. As described earlier thesingle stator lamination stack enables the flux sharing as illustratedin FIG. 7.

FIG. 8 illustrates a stator and rotor cross-section with an exemplaryarrangement for liquid cooling in the double-sided stator. In oneexample a liquid cooling channel 140 (or cooling duct) may be placedadjacent to the outer stator tooth 104. Liquid cooling channel 140, inone example is placed in the bottom of the slots formed between theouter stator tooth 104. The liquid used is typically at least one ofwater-glycol and de-ionized water, but any other liquid commonly usedfor cooling of electric machines may be used. Cooling channel 140 may beof any material used commonly for manufacturing cooling pipes, forexample but not limited to aluminum, copper, stainless steel or anycombination thereof. Cooling channel 140 may be connected in a range ofseries and parallel connections with one or multiple circuits. A heatexchanger (not shown) may be used to transfer the heat absorbed in thecooling liquid to the ambient air. Liquid cooling is advantageous sinceit provides a more compact machine that may be totally enclosed forprotection from the environment. In particular, in the examples ofliquid cooling described above, the net stator core thickness is reducedcompared to an air or wind cooled design. It therefore enables thediameter of the inner air gap 64 (FIG. 2) to increase, thereby enablingincreased power capability of the PM generator 12 for the same totaloutside diameter and axial length.

Also illustrated in FIG. 8 are pole caps 118 that are attached to eachof the air-gap-facing surfaces of the inner and outer permanent magnets,22 and 18, respectively. The pole caps are preferably of ahigh-resistivity, ferromagnetic, material such as asoft-magnetic-composite or bonded lamination stack. The pole capprovides mechanical protection to the permanent magnets, reduced rotor(magnet) losses, and also protection from demagnetization during faultconditions. The use of the pole caps 118 is not limited to liquidcooling, but may also be used in the prior PM generator embodimentsillustrated in FIGS. 1-7.

It would be appreciated by those skilled in the art that other coolingtechniques such as but not limited to forced-air cooling similar arealso equally applicable.

The double-sided generator 12 as described in different embodimentshereinabove, offers several advantages over single-sided generators forwind turbines. The most significant advantages include reducedmanufacturing and assembly costs, reduced stator mass, reduced machineouter diameter (thereby enabling land-transportation), and improvedbalancing of radial magnetic forces.

Although embodiments of the present invention have been describedprimarily in terms of wind turbines, the concepts are additionallyuseful in other applications with one example being ship propulsionmotors. FIG. 9 illustrates a sectional view of a portion of a shippropulsion pod unit 910 comprising an exemplary double-sided shippropulsion motor 912, a propeller 934, a mounting and bearing assembly936, and a frame assembly 938. The ship propulsion motor 912 includes arotor 914, including an outer rotor core 916 with outer permanentmagnets 918 and an inner rotor core 920 with inner permanent magnets922. The motor 912 also includes a double-sided stator 924 with an outerstator side 926 with an outer stator winding 928 and an inner statorside 930 with inner stator windings 932. The double-sided statorincludes a double-sided lamination stack 966 and is concentricallydisposed between the inner rotor core and the outer rotor core of theship propulsion motor. The double-sided lamination stack is configuredto enable the magnetic flux to flow radially between the inner statorside and the outer stator side. As in the wind turbine configuration,the inner stator side and the inner rotor core define an inner air gapand the outer stator side and the outer rotor core define an outer airgap

Many of the specific rotor construction details are similar to the windturbine embodiments and are not repeated here. The ship propulsion motormay also include a cooling duct for cooling the motor via passing aliquid cooling medium as shown in FIG. 8 with respect to wind turbine.The cooling duct may be an axial cooling duct in the double-sided statoror alternatively, the cooling duct may be located between at least twoadjacent stator coils of a respective stator slot. In a specific examplethe cooling duct may be located in a plurality of slots of thedouble-sided stator.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A wind turbine comprising; a wind turbine generator, the generatorcomprising: at least one rotor comprising an inner rotor core and anouter rotor core, wherein the outer rotor core is inverted with respectto the inner rotor core; and at least one double-sided stator comprisingan inner stator side including an inner stator winding and an outerstator side including an outer stator winding, wherein the at least onedouble-sided stator is configured to enable at least a portion ofmagnetic flux to be shared between the inner stator side and the outerstator side.
 2. The wind turbine of claim 1, wherein the inner statorside and the outer stator side comprise a double-sided lamination stackconfigured to enable the magnetic flux to flow radially between theinner stator side and the outer stator side.
 3. The wind turbine ofclaim 2, further comprising a plurality of axial bolts for providingcompression of the double-sided lamination stack.
 4. The wind turbine ofclaim 3, wherein the plurality of axial bolts are sufficiently longenough for mounting of the double-sided lamination stack to a stationaryframe.
 5. The wind turbine of claim 1, further comprising a cooling ductfor cooling the wind turbine generator via passing of at least one ofcooling air or a liquid cooling medium.
 6. The wind turbine of claim 5,wherein the cooling duct comprises an axial cooling duct in thedouble-sided stator.
 7. The wind turbine of claim 6, wherein the coolingduct is located between at least two adjacent stator coils of arespective stator slot.
 8. The wind turbine of claim 5, wherein thecooling duct is located in a plurality of slots of the double-sidedstator.
 9. The wind turbine of claim 1, wherein the inner stator sideand the inner rotor core define an inner air gap and the outer statorside and the outer rotor core define an outer air gap, and whereinportion of cooling air flows axially through the inner and outer airgap.
 10. The wind turbine of claim 1, wherein the at least onedouble-sided stator is concentrically disposed between the inner rotorcore and the outer rotor core of the wind turbine generator.
 11. Thewind turbine of claim 1, wherein the wind turbine generator is adirect-drive permanent magnet generator.
 12. A generator for a windturbine comprising: at least one rotor comprising an inner rotor coreand an outer rotor core; and at least one double-sided stator comprisingan inner stator side including an inner stator winding and an outerstator side including an outer stator winding, the inner stator side andthe outer stator side comprising a double-sided lamination stack,wherein the at least one double-sided stator is concentrically disposedbetween the inner rotor core and the outer rotor core of the generator.13. The generator of claim 12, wherein the double-sided lamination stackis configured to enable the magnetic flux to flow radially between theinner stator side and the outer stator side.
 14. The generator of claim12, further comprising a plurality of axial bolts for providingcompression of the double-sided lamination stack.
 15. The generator ofclaim 14, wherein the plurality of axial bolts are sufficiently longenough for mounting of the double-sided lamination stack to a stationaryframe.
 16. The generator of claim 12, further comprising a cooling ductfor cooling the wind turbine generator via passing of at least one ofcooling air or a liquid cooling medium.
 17. The generator of claim 16,wherein the cooling duct comprises an axial cooling duct in thedouble-sided stator.
 18. The generator of claim 16, wherein the coolingduct is located between at least two adjacent stator coils of arespective stator slot.
 19. The generator of claim 16, wherein thecooling duct is located in a plurality of slots of the double-sidedstator.
 20. The generator of claim 12, wherein the inner stator side andthe inner rotor core define an inner air gap and the outer stator sideand the outer rotor core define an outer air gap, and wherein portion ofcooling air flows axially through the inner and outer air gap.
 21. Thegenerator of claim 12, wherein the wind turbine generator is adirect-drive permanent magnet generator.
 22. A generator for a windturbine comprising; at least one rotor comprising an inner rotor coreand an outer rotor core; and at least one double-sided stator comprisingan inner stator side including an inner stator winding and an outerstator side including an outer stator winding, the inner stator side andthe outer stator side comprising a double-sided lamination stack,wherein the double-sided lamination stack is configured to enable themagnetic flux to flow radially between the inner stator side and theouter stator side, and wherein the generator is a direct-drive permanentmagnet generator.
 23. The generator of claim 22, wherein the at leastone double-sided stator is concentrically disposed between the innerrotor core and the outer rotor core of the generator.
 24. The generatorof claim 22, further comprising a plurality of axial bolts for providingcompression of the double-sided lamination stack.
 25. The generator ofclaim 22, further comprising a cooling duct for cooling the wind turbinegenerator via passing of at least one of cooling air or a liquid coolingmedium.
 26. A ship propulsion motor comprising: at least one rotorcomprising an inner rotor core and an outer rotor core; and at least onedouble-sided stator comprising an inner stator side including an innerstator winding and an outer stator side including an outer statorwinding the inner stator side and the outer stator side comprising adouble-sided lamination stack, wherein the at least one double-sidedstator is concentrically disposed between the inner rotor core and theouter rotor core of the motor.
 27. The motor of claim 26, wherein thedouble-sided lamination stack is configured to enable the magnetic fluxto flow radially between the inner stator side and the outer statorside.
 28. The motor of claim 26, further comprising a cooling duct forcooling the motor via passing of at least one of cooling air or a liquidcooling medium.
 29. The motor of claim 28, wherein the cooling ductcomprises an axial cooling duct in the double-sided stator.
 30. Themotor of claim 28, wherein the cooling duct is located between at leasttwo adjacent stator coils of a respective stator slot.
 31. The motor ofclaim 28, wherein the cooling duct is located in a plurality of slots ofthe double sided stator.
 32. The motor of claim 26, wherein the innerstator side and the inner rotor core define an inner air gap and theouter stator side and the outer rotor core define an outer air gap, andwherein portion of cooling air flows axially through the inner and outerair gap.